Fc receptors are integral plasma membrane, surface polypeptides of lymphoreticular cells, e.g., T-cells, B-cells, macrophages, monocytes,neutrophils, eosinophils, and basophils. The Fc receptors play a role in interaction and communication among these various cell types, and are perhaps involved in regulation of some of their physiological processes. The IgE-Fc epsilon receptor (FcER) interaction was selected for study, since this is likely to be a particularly important part of both anti-parasite immunity and IgE-mediated allergic responses. Eventually, by gaining some insight into the molecular nature of this binding interaction, one may better appreciate transmembrane signaling mechanisms and how they might influence subsequent biological function. The experimental approach will be to obtain molecular probes for the IgE heavy (H) chain and the FcER genes, their mRNAs and their proteins, using recombinant DNA and hybridoma technology. Mutagenesis of characterized, cloned DNAs will be used to construct defined, mutant genes to produce mutant proteins. The mutant proteins, together with monoclonal antibodies, will be employed to assess the importance of specific molecular domains in the IgE-FcER interaction. Mutant cell lines of the rat basophilic leukemia, RBL-1, deficient in their ability to bind IgE, will also be generated. The mutant cells will be used in transfection assays to study further and/or to correct the lesion(s) responsible for IgE binding defect(s). The mutants will also be used for cell fusions to restore IgE binding. Somatic cell, genetic analysis of such mutant-cell fusions will reveal functionally unique genetic elements, and thus define specific complementation groups necessary for cell surface expression of the FcER and its ability to bind IgE. Eventually, this work will expand our knowledge of the FcER and will aid in the understanding of how its synthesis and insertion into the plasma membrane is regulated. Finally, this study will provide a general, extremely valuable and very powerful approach for defining unknown genes and their products for complex transmembrane communication systems.